Back in November 2011, a multinational crew of six ended their 17-month long simulation to Mars and back. Confined to a trailer for 520 days, the pretend-astronauts had every detail of their lifestyle tracked, including their sleep-wake cycles, physical movements, intellectual activities, and light exposure. Now, looking at the results, it appears that the simulated journey had some noticeably detrimental effects, including a condition known as hypokinesis (decreased physical movement), an increased need for sleep, lack of motivation, and a lower tolerance for light — an indication that there's still lots of work to be done to prepare astronauts for a prolonged mission to the Red Planet.

Over the course of their simulated journey, the crew became increasingly sedentary, as shown by their decreased waking movements and increased need to sleep and rest. In addition, the majority of crewmembers also suffered from disturbances in sleep quality, an inability to stay alert and vigilant, and problems maintaining a natural circadian rhythm (one member fell into a 25-hour sleep cycle).

The volunteers moved less while awake and asleep, and spent more waking hours each day engaged in restful activities — playing video games, reading books, or watching movies. The crewmembers' wristwatches, which were equipped with light sensors, showed that the more lethargic they became, the more they shunned the lighted parts of the ship. By the final few months of the mission, three of the crewmembers slept about an hour more per day than they had at the beginning of the simulation.

The beds were small, recalls French crew member and flight engineer Romain Charles, and so narrow that he often had to sleep with his arm across his face. "I just had to learn to sleep like that," he says. But even though he adapted to the sleeping arrangements, it became difficult to take on intellectually laborious tasks, like improving his Russian language skills, in the final few months of the mission. Instead, he spent his spare time playing the video game Counter-Strike. "It really helped me get through that," Charles remembers.

It wasn't until the final 20 days of the mission that the crew, excited for their seclusion to finally end, became nearly as energetic as they were when the mission began.

This is problematic, of course, given the need for astronauts to stay alert and attentive at all times — especially in anticipation (or prevention) of an emergency.

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Moving forward, mission planners will have to take heed of the study's findings. Potential solutions include the introduction of more blue lighting to simulate conditions on Earth, including the effect of dawn and dusk. The crew could also adopt stricter schedules for both meals and physical activity. In addition, more work will need to be done to understand how to best treat sleep-wake cycles that have been thrown out of whack.

The study was published in the Proceedings of the National Academy of Sciences.